My recent exodus from Gmail and consequent return to the world of the desktop email client has got me thinking about what an email application really fundamentally is.It’s three things, it seems to me: it’s a text editor, it’s a database, and it’s a file manager. The problem is that there is no email client that fulfills all these functions really well. And probably no two users will weigh the relative importance of these functions in precisely the same way.Take Gmail, for instance. It has always been an extremely responsive, extremely reliable database. And as its system of labels, filters, and “Labs” commands developed — Oh how I miss you, Send and Archive! — it became an increasingly sophisticated file manager. But its text editing capabilities were limited and awkward from day 1. As much fun as it was to set up an organizational system in Gmail, it was that much of a pain to write anything in the darn thing.Contrast that to an ancient favorite of the geeky Mac crowd, Mailsmith — none of that newfangled IMAP crap for me, sonny! — which borrows its text-editing engine from BBEdit and therefore in this respect blows every other email client in the world out of the water. It has a pretty good filtering system too, with fine-grained controls, though in my experience the filters do not work consistently. But its database, while solid, is excruciatingly slow — I mean, go-out-and-have-lunch-and-it-still-hasn’t-finished-your-search slow — so that and its single-minded devotion to POP make it unusable.If swift and sophisticated file management is your sine qua non, then you can’t do better than — well, mutt or alpine, assuming you don’t mind working from the command line. Watching a true mutt master compose, send, reply to, and file emails is like watching the knife tricks at Benihana. But mutt and alpine obviously aren’t serious options for many users.So we’re still waiting, I think, for an email app that puts it all together. Maybe Letters, the early-in-development email client for alpha Mac geeks, will do it. But I doubt it. My guess is that email will be replaced by a wholly different communications technology before anyone figures out how to make an email client that isn’t seriously compromised in one or more of its functions.